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-   -   External FastMem with a TF534 (http://eab.abime.net/showthread.php?t=102360)

psoma 23 May 2020 03:18

External FastMem with a TF534
 
Hi,

Am looking at getting myself a TF534 accelerator, but currently have a SCRAM 500 with 8MB Autoconfigure RAM. Had a couple of questions I'd like to run past the brains trust...

1) So the TF534 has 4MB of 32-bit RAM. If I disable 4MB in my SCRAM500 (it can run as 0, 2, 4 or 8MB), will Autoconfigure automatically pop 4MB from the TF534 and 4MB from the SCRAM500 in the correct memory addresses, or will they overlap?

2) If the former, will the system preference the 32-bit FastMem over the 24-bit sidecar FastMem?

Cheers!

hooverphonique 23 May 2020 16:59

I think the TF uses proper auto-config, so you shouldn't get an overlap - some of the TF's support using an address range outside 24 bits for its onboard ram (so you could keep all 8MB of SCRAM) , don't know about the 534 though.
Regarding the preference, it's entirely up to the priority the developer uses when the memory is added to the system - you can look up the priority of your SCRAM memory using something like SysInfo.

psoma 24 May 2020 00:25

Thanks mate - so looks like the TF534 autoconfigures to Zorro III (530 did not), and I just read the SCRAM technical details (God bless the 80s/90s and their desire to share every intricate detail with us):

"Note that BORIS looks at the RAM SIZE jumpers JP1, JP2 to tell the Amiga
how much RAM is available (0/2/4/8 Meg). The DENNIS chip latches the RAM
BASE OFFSET at AutoConfig time. DENNIS then becomes the address space
decoder for RAM, selecting the four banks in ascending order.
The Amiga always allocates RAM from 200000 onwards. None, 2, 4, 8 Meg
are possible configurations. When other RAM devices precede the SCRAM,
the base offset will not be 200000, so note that some memory sizes will
be illegal. Most likely just 8 Megs, as this needs ALL the RAM space to
configure."

Seems like it is compatible, even if the TF534 mapped to Zorro II (I'd just have to disable 4MB on the SCRAM).

Off to market I go...

jbilander 24 May 2020 11:41

The TF534 will autoconfig to Z3 space so shouldn't conflict. I think the TF534's 4MB 32-bit RAM will be given higher priority config automatically but I'm not sure. That is however important because the accelerator CPU has to insert wait states when talking to the 7 MHz bus (glue logic) = slow, whilst when talking to the 4MB onboard SRAM it is a matter of "don't tell the Amiga about it" and run full speed. The TF534 is obsoleted/not worked on any more and replaced with the TF536.

psoma 25 May 2020 02:01

Yeah, I've ordered a TF534 for now and will report back on the autoconfigure/priority situation. I realise the TF536 is the going concern but my understanding is there are no pre-built boards available yet, so the TF534 will (hopefully) tide me over until I upgrade to the TF536 down the track.

Cheers all!


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